Fixed-node quantum Monte Carlo for molecules
The ground-state energies of H/sub 2/, LiH, Li/sub 2/, and H/sub 2/O are calculated by a fixed-node quantum Monte Carlo method, which is presented in detail. For each molecule, relatively simple trial wave functions Psi/sub T/ are chosen. Each Psi/sub T/ consists of a single Slater determinant of molecular orbitals multiplied by a product of pair-correlation (Jastrow) functions. These wave functions are used as importance functions in a stochastic approach that solves the Schroedinger equation by treating it as a diffusion equation. In this approach, Psi/sub T/ serves as a ''guiding function'' for a random walk of the electrons through configuration space. In the fixed-node approximation used here, the diffusion process is confined to connected regions of space, bounded by the nodes (zeros) of Psi/sub T/. This approximation simplifies the treatment of Fermi statistics, since within each region an electronic probability amplitude is obtained which does not change sign. Within these approximate boundaries, however, the Fermi problem is solved exactly. The energy obtained by this procedure is shown to be an upper bound to the true energy. For the molecular systems treated, at least as much of the correlation energy is accounted for with the relatively simple Psi/sub T/'s used here as by the best configuration interaction calculations presently available.
- Research Organization:
- National Resource for Computation in Chemistry, Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720
- OSTI ID:
- 6705530
- Journal Information:
- J. Chem. Phys.; (United States), Vol. 77:11
- Country of Publication:
- United States
- Language:
- English
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HYDROGEN
ELECTRONIC STRUCTURE
LITHIUM
LITHIUM HYDRIDES
WATER
ENERGY
GROUND STATES
MOLECULES
MONTE CARLO METHOD
QUANTUM MECHANICS
WAVE FUNCTIONS
ALKALI METAL COMPOUNDS
ALKALI METALS
ELEMENTS
ENERGY LEVELS
FUNCTIONS
HYDRIDES
HYDROGEN COMPOUNDS
LITHIUM COMPOUNDS
MECHANICS
METALS
NONMETALS
OXYGEN COMPOUNDS
640302* - Atomic
Molecular & Chemical Physics- Atomic & Molecular Properties & Theory